Integrated micro-optical elements have played a central role in data storage, optical displays and imaging systems. Fine alignment and focus adjustment in these systems is usually performed by means of mechanical parts that are often expensive, fragile and slow.
To overcome limitations introduced by mechanical adjustment, different electrical based inventions have been proposed. A first strategy relies on reshaping the surface of a liquid using an electrical signal without altering the thermo-optical properties of the material. For instance, the electro wetting lens described in U.S. Patent Application Publication No. 2013/0194323 demonstrates that the shape of a liquid drop can be modified by applying a voltage. The local voltage applied to the surface changes the contact angle between the drop and the surface, thus modifying the shape of the drop, which results in a change of the focal point associated to the liquid based micro lens. Nevertheless, such an approach suffers from drawbacks, which include (but are not restricted to) difficulties of integration, slow time response (in some applications, acceleration of the system could alter the shape of the drop and introduce imperfections in the lens) and inability to simultaneously image multiple planes with a single lens.
A second strategy uses an electrical excitation to deliver energy which alters a lensing material, placed between two electrodes, and tunes its properties. Following this strategy, an electrically excited thermo-optical lens as disclosed in U.S. Patent Application Publication No. 2005/0117195 has been invented. In this patent, a thermo-optical polymer is enclosed between two optically transparent surfaces, one of them curved, and a temperature controller is coupled to the thermo-optical material. Although this lens allows for the change of focal property, it does not allow for finer control such as local adjustment of the focal point. Furthermore, when considering this invention in a matrix configuration, there is a need to electrically address each lens, which could result in a complex engineering of the lens system, prohibiting its use in some applications.